Circulation March 28, 2017 Issue

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Caroline: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr. Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore. Up next, we are discussing the featured paper in this week's journal regarding the increased risk of cerebrovascular events in young cancer survivors, the downside perhaps of surviving cancer, so to speak. But first, here's your summary of this week's journal.

The first paper describes the US national trends in atrial fibrillation hospitalization, readmission, and mortality. This paper from Dr. Freeman and colleagues of Yale University School of Medicine in New Haven, Connecticut used data from all Medicare fee-for-service beneficiaries between 1999 and 2013, and found that the adjusted rates of hospitalization for atrial fibrillation increased by almost 1% per year. Median hospital length of stay remained unchanged at three days, but median Medicare inpatient expenditure per beneficiary increased from $2,932 to $4,719 per stay.

During the same period, the rate of inpatient mortality during hospitalization for atrial fibrillation decreased by 4% per year, and the rate of 30-day readmission also decreased by 1% per year, while the rates of 30-day and one-year mortality decreased more modestly by 0.5% and 0.26% per year, respectively. Thus, between 1999 and 2013, among Medicare fee-for-service beneficiaries, rates of hospitalization for atrial fibrillation and the cost of those inpatient stays increased substantially, but this was associated with improved outcomes, including lower rates of readmission and mortality. These findings suggest that increased hospitalization and more costly contemporary treatments, such as atrial fibrillation catheter ablation, may be associated with improved outcomes.

The next study provides insights into the mechanisms underlying augmentation of muscle blood flow by ultrasound cavitation of microbubbles. Now, this is a promising approach for rapidly correcting tissue profusion in acute ischemic syndromes or for treating chronic ischemic symptoms. In this paper by first author Dr. Belsik, corresponding author Dr. Linder, and colleagues from Night Cardiovascular Institute Oregon Health and Science University in Portland, Oregon, the authors hypothesized that pure endergic signaling may be responsible for sheer dependent increases in muscle profusion during therapeutic ultrasound cavitation.

To test this hypothesis, the authors studied unilateral exposure of the proximal hind limb of mice with and without ischemia produced by iliac ligation, to therapeutic ultrasound after intravenous injection of lipid microbubbles. They further performed a proof of concept study with twelve patients with stable sickle cell disease. They found that therapeutic ultrasound cavitation increased muscle profusion by seven-fold in normal mice, reversed tissue ischemia for up to 24 hours in the murine model of peripheral artery disease, and doubled muscle profusion in patients with sickle cell disease.

Augmentation inflow extended well beyond the region of ultrasound exposure. Ultrasound cavitation produced a nearly forty-fold focal and sustained increase in ATP, the source of which included both endothelial cells and erythrocytes. Inhibitory studies indicated that ATP was a critical mediator of flow augmentation. Furthermore, combined indomethacin and inhibition of eNOS abolish the effects of therapeutic ultrasound, indicating downstream signaling through both nitric oxide and prostaglandins. Thus, the authors concluded that therapeutic ultrasounds using microbubble cavitation to increase muscle profusion relies on sheer dependent increases in ATP, which can act through a diverse portfolio of purinergic signaling pathways. Cavitation-related release of ATP may further serve to explain ultrasound's role in other therapeutic applications, such as wound and bone healing, and ultrasound facilitated drug or gene uptake.

The final original paper describes the age-specific trends of heart failure in Denmark over the last two decades. Dr. Christiansen and colleagues of University of Copenhagen in Denmark studied more that 210,000 Danish individuals over the age of 18 years, with a first time in-hospital diagnosis of heart failure from three nation-wide Danish registries.

They found that the incidents of ischemic and non-ischemic heart failure in Denmark declined by approximately 50% among older adults more than 50 years old, but increased by about 50% among younger individuals, or individuals less than 50 years old, between 1995 and 2012. Furthermore, they observed a concomitant increasing trend of various treated co-morbid conditions, including hypertension, diabetes, and ischemic heart disease in the population. These findings from Denmark imply a change in the profile of the heart failure community and portend a higher burden of heart failure in the future. The increasing trend of incident heart failure among young individuals especially warrants further investigation.

Well, those were the original papers this week. Now, for our feature discussion.

Our feature paper today discusses a hugely important modern issue that may seem like good news at first sight. We know that survival in cancers has rapidly improved with advances in early detection and treatment, however the improved survival also extends the window for the occurrence of long-term complications such as psycho-social effects, fertility problems, secondary malignancies, and, as highlighted in today's paper, the risk for cerebrovascular events. I'm so pleased to have with us first, author Chloe Bright from University of Birmingham, United Kingdom, as well as associate editor Dr. Graeme Hankey from University of Western Australia. Welcome, Chloe and Grim!

Chloe Bright: Thank you for having me.

Graeme Hankey: Thank you Caroline.

Caroline: Chloe, what an interesting and important focus on cerebrovascular events following survival from cancer. Please, can you share your inspiration for looking at this and what you found?

Chloe Bright: As you've just said, the five year survival rate from teenage and young adult cancer has been increasing and increasing, and it's over 80% now, which means there's such a large population of survivors who are at increased risk, or potentially increased risk, of developing adverse health outcomes. So, as you know, cerebrovascular disease can be potentially fatal so it's really important that we estimate how much teenage and young cancer survivors are at risk of this. So to start of with our group in Birmingham actually set up the teenage and young adult cancer survivor cohort study. And this is a cohort of over 200,000 five year survivors of cancer who were diagnosed between 15 and 39 years of age. And this was set up because there's hardly any literature regarding the adverse health outcomes of teenagers and young adults who have had cancer.

So, as I said, cerebrovascular disease is a really important outcome to look at. So we decided we've got this resource in the UK, which is the Hospital Episode Statistics, and this carries information on all the inpatient hospitalizations in England. So from this we were able to determine how many people with teenage and young adult cancer had been hospitalized for cerebrovascular events and compare this to what we would expect to see in the general population to see if they had an increased risk or not. So from limited previous literature that was out there we did know that TYA cancer survivors had an increased risk of developing a cerebrovascular event. However, we were unsure how this risk varied with certain explanatory factors, such as age of cancer diagnosis or the decade of cancer diagnosis, gender, and attained age, so that's the age at which a stroke event might occur. So the main aim of our study was to quantify this.

Caroline: Yes and to put some numbers to that increased risk. It was a 40% increased risk, wasn't it? That is striking.

Chloe Bright: We observed almost 2,800 cerebrovascular events. That related to a 40% increased risk of being hospitalized compared to what we would expect to see in the general population, which is really quite substantial.

Caroline: Now, were there particular risk factors that were associated with more cerebrovascular complications like certain types of tumors or certain types of therapies and so on?

Chloe Bright: Survivors of central nervous system tumors, head and neck tumors, and leukemia were all at the greatest risk compared to the general population. And this is probably related to radiotherapy that they had for their initial treatment. So radiotherapy to the neck, which could involve damage to the carotid artery, or radiation to the head which again could cause damage to the cerebral arteries in the brain. And then also we found that the risk increased dramatically as people aged for neck tumor survivors and CNS tumor survivors. So specifically cerebral infarctions, the additional number that we saw was a lot greater in, say, survivors over age 60. And this is probably because this is when strokes in the general population are becoming more incident.

And actually an interesting finding, we observed that males actually had a higher number of excess infarctions than females, and this was especially among head and neck tumor survivors. So we can't confirm this, but this could potentially be due to difference in smoking habits because there could be a said etiology between smoking and the risk of head neck cancer and also smoking and the risk of stroke. Unfortunately, we didn't have the information on smoking status to confirm this.

Caroline: This is a huge study. It shows a substantial increased risk of stroke in these young cancer survivors, and also sheds light on the possible underlying mechanisms. What you mention about vasculopathy following radiotherapy really reminds me about what we learn about breast cancer radiotherapy and the risk of myocardial infarction.

Graeme, what are your perspectives on this paper please?

Graeme Hankey: Well as an editor, as everyone knows, what we're really looking for are four main points. Firstly that the study was ethical, which it was. Secondly that the results are valid, internally and also externally. And we're very confident in the validity of the results. This was a very large study of 180,000 people, and more importantly had 2,800 cerebrovascular events so that's a lot of [inaudible 00:12:25] and the followup was pretty rigorous over 11 years, and the outcome events were [inaudible 00:12:32] by a data linkage through the hospitalization for the cerebrovascular events.

The other two key features of course is are the results novel and are they important? And these are novel results. There's only been one previous similar study of a Danish cohort that was only 43,000 but one quarter the size of this study, and one year survivors of teenage and young adult cancer from 1943 to 2009 and followed up. And the results were actually very similar, showing a 1.3 or 30% increased risk of hospitalization for cerebrovascular events. Again supporting the validity of this recent study to obtain similar results, but in a four times greater population and in a more contemporary population whose patients were recruited between 1971 and 2006 and followed up from 1997 to 2012.

And the other thing is it's not just ethical, valid, and novel, but it's important because it really has big implications for stroke prevention in young adult survivors of cancer. And it has implications for once they get the diagnosis and they're through their treatment to really focus on what were their pre-morbid vascular risk factors? Are they actually causal risk factors and not just cancer but also for future stroke like smoking and alcohol, and hypertension and diabetes? Secondly to try and recognize what is their absolute risk? Are they men who are at higher risk? Have they had previous irradiation that probably puts them at higher risk, as well as their current respective profile?

Thirdly for them to then realize what's the impact of their cancer diagnosis on their future behaviors if they become depressed or change their diet or taking other treatments, or abusing drugs, and could that increase their vascular risk? And fourthly, what should be done? Should they just control their vascular risk factors through lifestyle? Or should we actually have a randomized trial of risk factor control, and/or antiplatelet therapy and/or statins and/or blood pressure lowering in these high risk survivors of cancer who are sill in their forties or fifties. Should they actually be taking antiplatelet therapy or statins? We probably need a randomized trial because they're high risk, we would think, or certainly a sub-population.

Caroline: Thanks Graeme for framing that so excellently. You're absolutely right that these are the things we look for in a paper as editors. And for our listeners to hear that is just so important.

Well, I'd like to hand it over to you now Chloe. What are the next steps in your mind? What are the remaining gaps in knowledge you'd like to address?

Chloe Bright: I really think it relates to what Graeme just said. We need to get the information on the specific radiotherapy, the doses that have been used, the potential lifestyle factors of these individuals to see how much of an effect that has on the risk of stroke. So potentially conduct a case control study while we're able to get this information and then use that. And then, as Graeme said, once there is more information potentially a randomized control trial might be useful. But again, I think we need some more information before we can get the go ahead to doing that.

Caroline: Great. Just one more quick question please. You know, Chloe, you found that those who were more recently treated had a higher risk of cerebral hemorrhage than among survivors diagnosed earlier. Now, did you have any postulations on why this was the case?

Chloe Bright: This increase in the hemorrhage with more recent diagnosis was actually restricted to glial tumor survivors. So one explanation that we thought might explain this was that in recent years due to advances in treatments those glial tumor survivors, glial tumors who had more advanced stage at diagnosis, potentially surviving a little bit longer, so reaching five year survival which would enter them into our study. However they potentially might be having another occurrence, which would be causing them to have a hemorrhage, which in the previous decades perhaps they wouldn't have survived that long in the first place. That's just one of many ideas.

Graeme Hankey: I think the recurrence of not just glioma but perhaps also melanoma that the survival is much greater now with new immunomodulating therapies for melanoma, we'll probably see longer survival in melanoma which typically when it metastasizes is hemorrhagic and perhaps also leukemia with thrombocytopenia, with more hemorrhage and other metathesis. The other thing it could be though is a diagnostic ascertainment bias in that I'm 60 now, and when I started neurology 35 years ago we didn't really have much brain imaging and couldn't diagnose intracerebral hemorrhage very well. And clinical diagnosis wasn't very reliable. Now the imaging which can actually distinguish hemorrhagic from ischemic stroke is much more widely available. And I suspect there's a greater increase in the diagnosis of cerebral hemorrhage now because of better imaging. We've seen that in other epidemiologic studies with that diagnostic trend.

Caroline: What excellent points. Thank you so much Chloe and Graeme.

Well you've been listening to Circulation on the Run. Thanks for joining us today and don't forget to tune in next week.

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